O,O-diethyl phthalimidophosphonothioate, methods for its preparation, and teachings of its utility as a pesticide and as an active toxicant in compositions for the control of insect, mite, helminth, plant fungal and bacterial organisms are described in U.S. Pat. Nos. 3,336,188; 3,450,713; 3,803,167; and 3,853,909. The method taught by the first two of the above patents basically entails the reaction of an N-alkali metal phthalimide with O,O-diethyl phthalimidophosphonothioate in the presence of an inert amido reaction medium such as, for example, N-methyl-2-pyrrolidone, dimethylformamide, hexamethylphsophoramide, N-acetylmorpholine and dimethylacetamide.
U.S. Pat. No. 3,803,167 teaches another method of preparing O,O-diethyl phthalimidophosphonothioate wherein O,O-diethyl phosphorochloridothioate is reacted with N-alkali metal phthalimide in the presence of an aromatic tertiary amine catalyst, such as pyridine, alpha-picoline, dimethylaniline, triphenylamine, pyrazine and quinoline, and a tertiary alcohol as solvent or reaction medium. Aliphatic tertiary amines were not found to be useful as catalysts in the process of U.S. Pat. No. 3,803,167.
U.S. Pat. No. 3,853,909 teaches preparing O,O-diethyl phthalimidophosphonothioate by reacting O,O-diethyl phosphonochloridothioate N-alkali metal phthalimide in the presence of a catalytic amount of 1,4-diazabicyclo-(2,2,2)octane and an inert tertiary alcohol as a solvent or reaction medium.
U.S. Pat. No. 3,399,213 teaches several methods of preparing O,O-diethyl phthalimidophosphonothioate. In one method, O,O-diethyl phosphoramidothioate is reacted with phthalic anhydride in the presence of dimethylformamide reaction medium and sodium hydride under a nitrogen atmosphere.
The above-described processes effectively produce the desired phosphonothioates. However, the process of the present invention is desirable in that it utilizes readily available starting materials while producing the desired phosphonothioate in good yields. The present process is particularly advantageous over the process described in U.S. Pat. No. 3,399,213 because the sodium hydride, which is hazardous, difficult to handle and nonrecoverable is replaced by a tertiary amine catalyst which is recoverable, easily handled, and less hazardous than sodium hydride.